Patent GB-634691-A (GB)
Title: Improvements in and relating to ground aviation trainers
IPC: G09B9/24
Filed: 1947-08-25
Abstract: 634,691. Ground trainers. LINK AVIATION, Inc. Aug. 25, 1947, No. 23435. Convention date, Aug. 24, 1946. [Class 4] [Also in Group XXXVIII] A ground trainer is provided with a dummy magnetic compass arranged to simulate " northerly turning error " due to turning of the fuselage, the compass indicator element being subjected to two superimposed movements, one being determined by the assumed course or heading of the fuselage and the other by the rate of turning of the fuselage. General arrangement.-The invention is showii as applied to a trainer of the type described in Specifications 370,128 and 481,375, in which the attitude of the fuselage is controlled by oppositely disposed pairs of bellows, and the fuselage is turned by a suction-operated motor upon actuation of the rudder pedals which, through links 48, 51, control a valve 56 connected to the suction source 66 by a pipe-line 64. The needle 134 of the dummy compass is operated by the receiver 124 of a Selsyn transmission, of which the transmitter 115 is connected to the compass by a cable 122, and the housing 114 is rotated by a pinion 110 at one end of a shaft 94, the other end of which carries a pinion 96 meshing with a fixed gear ring 90 bolted to the fuselage support. The compass reading as determined by the heading of the fuselage is modified, to introduce the turning error, by bellows 238, 246, controlled by a " course " valve 192 connected thereto by pipes 234, 242, and a " rate of turn " valve 168 connected to the valve 192 by pipe-lines 190, 196. A shaft 386 connects the housing 114 and the rotary element of the valve 192, so that the setting of the latter is determined by the orientation of the fuselage. The valve 168 is connected to the suction source 66 by a pipeline 182, and has a connection to atmosphere, 186; its rotary element is controlled by a link 140 connected to the link 52 operating the rudder control valve 56, so that its displacement is proportional to the rudder pedal movement, i.e. to the rate of turning of the fuselage. Movements of the bellows 238, 246 result in rotation of a member 308 connected by a pin 312, a spring centring device 319 and a spring coupling 338 to the Selsyn transmitter rotor 138. Operation.-The trainer fuselage is assumed to be turning from an initial due-west heading, through south, east, and north. In the initial position, with the rudder pedals centred, the rudder valve 56 and rate valve 168 are in their neutral positions, while the course valve 192 is 180 degrees from the neutral position. Upon moving the left rudder pedal the valve 56 is operated to turn the fuselage, while the rate valve 168 is rotated counter-clockwise to apply suction to the line 190 and atmospheric air to the line 196. Rotation of the fuselage causes counter-clockwise rotation of the course valve 192, to apply increasing suction to the bellows 238, and increasing pressure to the bellows 246, resulting in clockwise rotation of the member 308 and thus of the Selsyn transmitter rotor 138. Since the transmitter housing and rotor are turned in opposite directions, their relative angular displacement at any instant is greater than the departure of the fuselage from due west, and the compass needle reading is thus in advance of the true fuselage heading. The extent of the lead increases until the fuselage heads due south, after which the course valve 192 reduces the degree of suction applied to the bellows 238 and the pressure applied to the bellows 246, thus reducing the lead of the compass needle. When the fuselage heads due east the valve 192 is closed and there is no discrepancy between the compass indication and the fuselage heading. As the fuselage turns on a northerly course, the application of suction and pressure to the bellows 238, 246 is reversed, and the transmitter housing and rotor turn in the same direction, thus producing a lag in the compass reading, which reaches a maximum when the fuselage points due north, and falls to zero when it returns to the due west heading. To simulate conditions in the southern hemisphere the pipelines 190, 196 are reversed, while the effect of latitude may be simulated by varying the effective length of the arm 148 controlling the rate valve 168. The oscillations of the compass needle produced by taking an aircraft out of a turn when on a course differing from that shown by the compass is also simulated by the provision of a flywheel 382 carrying braking vanes 384, and geared through step-up gearing to the pinion 366 connected to the spring coupling 338. Upon centring the rudder pedals the rate valve 168 and the bellows 238, 246 are brought to the neutral position, 'the gear wheel 366 also being centred by the spring assemblies 319, 338. The wheel 366 rotates towards the neutral position relatively slowly, but the step-up gearing between it and the flywheel 382 causes the latter to rotate at a high speed and thus carry the wheel 366 beyond its central position. Under the influence of the flywheel and the spring assemblies the wheel makes several oscillations before coming to rest, with consequent oscillation of the compass needle. Specification 611,304 also is referred to.